The Determined Hero
by ef9283
Summary: Shirou's only dream was to save everyone. To be a Hero of Justice. His fight against Archer had forced him to accept he can't, but Shirou never gave up trying to save as many people as he could. What happens when he falls into a world where he could fulfill his dream? Is he be too distorted to see it?


I yawned.

I had left the village of Mendi early in the morning, hoping to reach Mt. Ebott in time to make a decent shelter. I had failed. The mountain itself could be seen from the village, but once I had finally gotten into the forest surrounding Mt. Ebott, it became nearly impossible to see where I was going. It also didn't help that my bag had caught on a branch a short way in tore itself open. Or that I was only able to carry a few energy bars with me deeper into the woods due to my armor not having any pockets. A few hours of wandering blindly, climbing trees to see where the mountain was, and several projected compasses later, I had finally reached Mt. Ebott.

And I couldn't find a way up from where I was.

So I had to skirt around the mountain looking for anything that could be considered a path, which took a few hours more. Finally, I found a way up, and had started climbing. It wasn't until I got above the tree line until I realized how late it was. I had maybe an hour before sunset. And so I tried to climb even faster, searching for a cave or level area I could stay for the night. Unfortunately, there wasn't any. Trees sparsely populated the incline I had found, and the entire area was just too open to the sky. If there was something on Mt. Ebott, I didn't want to be caught by it because I feel asleep in the open. I had to keep climbing. I took a short break, and finished my provisions before I resumed my climb. And now the sun was setting, while I was halfway up a mountain said to contain monsters, with no supplies or a safe place to sleep.

I can almost hear Archer laughing at me, but I'm determined make sure this place is safe.

I had been traveling along east Africa helping whoever I could when I ended up in a small village in Ethiopia. I spent a couple days helping around town with a few small things, when I heard of Mt. Ebott for the first time. According to the villagers, a long time ago monsters lived with humans, until a war drove them all to be contained in Mt. Ebott. The villagers seemed to really believe Mt. Ebott was home to monsters, and insisted that I stay as far away as possible. They told me over and over that no one who had ever gone to investigate the mountain had ever returned. So of course, I set out to investigate.

I'm no stranger to monsters. As a Hero of Justice, I run into them all the time. I've fought everything from Dead Apostles who feast on the blood of humans to territorial Phantasmal Beasts to a really arrogant heroic spirit and even a battle against ORT after a greedy magus went and pissed it off. So I came to make sure whatever resided in this mountain wasn't a threat to humanity, and if it proved itself to be dangerous, eliminate it. Or see if there was anything here.

Because it didn't seem like there was anything here at all.

One of my talents was magic detection, which manifested itself as a smell. When I was younger, my friend Rin described my sense of smell as "like a blood hound", which was not a bad description. I've used this ability for years to detect and track magic, and I've been paying attention the entire trip, smelling for any signs of magic. If there really was a bunch of monsters living here, I likely would have noticed it a while ago. The forest lacked any kind of magic traces and there seemed to be nothing this far down Mt. Ebott. So unless there was something further up, this was probably a waste of time. Unfortunately, that wouldn't be enough to safely say there was nothing here. I'll probably spend the next few days here checking the surrounding areas for magic.

I sighed pitifully and stopped climbing. I took a minute to look around. There was still nowhere safe to rest. Only a couple of trees scattered across the place, on inclines too steep to safely sleep on. It would probably take about thirty minutes to get close enough to the summit to be sure there was nothing suspicious. The sun had just fallen below the horizon, so I had maybe an hour before things started getting really dark. Looks like I was going to have to make a choice. Go back down to the forest and climb in the morning, or keep climbing and hope there was somewhere decent to sleep further up. I really didn't fancy sleeping in the forest, but if I couldn't find a place at the top, I'd have to climb back down in the dark and sleep there anyway. I yawned again. Surely there is something up there right? I let loose another sigh. Who am I kidding.

"Maybe if there is some kind of monster here, it would let me sleep in its den." I muttered. "I could probably convince it by offering to cook for a couple days."

If there was one thing I was unrivaled in, it was my skill in the kitchen.

Resigned to my fate, I continued my climb.

Since I had started traveling a few years ago, things had really slowed down for me. Every now and then, I got a call from the clock tower of some Apostle Hunt they wanted my help with, or something they wanted me to investigate, but they were becoming more and more rare. There were a lot fewer Apostles today then there were when I was a kid. Of the twenty seven Apostle Ancestors, only ten were still free. The rest were either sealed by the church or slain by me. It had taken me over a decade to hunt the most dangerous ones down, even the ones not know to the church, and doing so had netted me some powerful enemies. Altrouge Brunstud swore to 'bring me to justice' for assassinating two of her bodyguards.

Ten minutes pass. Only a little further to go.

Altrouge was a strange one. She acts like magic girl, but has considerable sway with the other dead apostles. I had nothing really against her though, despite how much she terrifies me. I feel like my soul was in danger every time I've seen her. Despite her threats, she wasn't the one to try to kill me. It was her sister. Arcueid had confronted me while I was traveling around Japan. Of the many brushes with death I've had over the years that had probably been the closest.

I had no intentions of killing her, I had heard her story from a few different sources, and I knew she was not hostile to humanity. She had every intention of killing me though. Lucky, sometime during the fighting I managed to convince her I was only hunting the apostles that were either hostile to humans or killed them regularly. She wasn't particularly happy about it, but she let me go in one piece. I even convinced her to seek out and take care of her sister.

In return she told me Trhvmn Ortenrosse was the one who sent her after me. That was fine. I was going to go after him soon as well. He had been working for years to weaken humanity for the Crimsons Moon's return, and he was high on my list to kill.

After returning to the Clocktower, Lorelei and I got along real well after I told her who my next target was. She helped me hunt him down personally. His death had probably been the reason I wasn't granted a sealing designation when news about my reality marble go out.

I yawned again. Twenty minutes pass. Almost there.

Then I froze. I had crossed a bounded field; I could feel the change in the air. This alone would have been shocking, but then I took a breath. The magic in the air was staggering.

There was something big here. And that something was being protected by a Magus. Had I intruded on someone's workshop? Was this some Apostle base? What does this bounded field do? I cursed under my breath; I had to keep climbing didn't I? I was now on the side of a mountain, with no supplies, exhausted from travel, in enemy territory, and it was dark. Damn my E rank luck.

I nearly traced Bakuya and Kanshou, but if I was being watched by whoever created this field, I didn't want to give away my abilities. I also couldn't just go back down the mountain. Now that I've entered this bounded field it's likely someone knows I'm here, so if I back off to sleep I could be attacked while I was unprepared.

I need to confront whoever created this now.

Taking another sniff, I could tell the source of the field was not at the summit. It was coming somewhere from my right, a little further up around from where I could see. I reinforced my legs, and sprinted towards the source. I reached my destination in seconds, a cave secluded by trees. The field was being created by something inside there.

"Trace On." I whispered.

The imaginary gun in my head fired. I dashed forward preparing to trace Bakuya and Kanshou.

And tripped.

In my defense, it was really dark. And that branch was surprisingly sturdy. And I was tired.

I tumbled headfirst into the cave, flailing wildly, trying to roll to regain my foothold and recover. Unfortunately, the inside of the cave was a downward slope, and rolling just made my fall even worse. My feet landed on some loose rocks and I continued my tumble. My eyes darted about looking for anything that could be a threat, but it was just too dark to make anything out. Suddenly, I realized I wasn't bumping into anything anymore. A feeling of vertigo hit me. My hands shot out, looking for something to prevent falling off wherever I was. My hand clenched around what felt like a vine, before I heard it snap. Cursing, I reinforced my body as best I could before I hit the bottom.

Suddenly, I could feel some kind of magic surrounding me. Great, I hadn't just fallen into a hole. I fell into a _magic_ hole, and whatever this magic was doing was making it hard to stay awake. I needed something to break this spell. The first sword that came to mind was Rule Breaker. I started feeding my Od through my magic circuits. Just a second more and I'd have a chance to escape.

But I was too slow, the magic finished surrounding me. Falling into some unseen pit, I lost consciousness.

* * *

 **Thank you for reading the first chapter in my story!**

 **I'm not great at writing, but with most disciplines, practice is the only way to improve. I had some free time with college being out for break, so I decided to write a story that's been floating around in my head for a while. I was browsing the Undertale crossovers and saw that there wasn't a crossover for Fate/Stay Night yet, which seemed strange to me. The more I thought about it, the more the worlds fit together. I can only hope to do both worlds justice.**

 **I'll also use the area down here to describe some of my choices in regards to this story. Some of these explanations will contain minor spoilers, so if that is a concern for you, first why are you reading a fanfic, and second go play Undertale. It's worth it.**

 **Why is Mt. Ebott in Ethiopia? – There were a number of things that put Mt. Ebott there for me. First was it couldn't be anywhere too developed. If it was, it would have been explored to death by the people around it. So I dropped India, China, Europe and North America of the list as possible places. Second is the name of the first human to drop down. Chara sounds Greek to me, and according to the Undertale lore, she came down a** _ **long**_ **time ago. So I figured sometime shortly after Alexander the great was as good a guess as any. So I narrowed it further. Beyond that Ethiopia is extremely mountainous, so I could imagine it being in there. In addition it's in Africa, so humans would have arrived in the areas populated by monsters very early on, which fits well with the story. It doesn't explain the radically different children that seemed to fall down into the underground, but I'm not sure anything could unless time is completely different down there or there are multiple entrances. Also for the nasuverse I wanted Mt. Ebott in a place a magus probably wouldn't have found. The only reason Shirou heard of it is because he was helping around in a village. In the long run, the location won't matter much story wise anyway.**

 **Which Shirou is this? – It's an altered Unlimited Blade Works Shirou. I'm not going to explain much more than that here, but it will be a plot point later on. Age wise I'd place him around late 30's when the story starts. Clothing wise he wears stuff very similar to Archer, it's just the best stuff he could find for what he does.**

 **How and why did Shirou kill so many apostle ancestors? – This will be a plot point later as well, but I imagine it as something Shirou would do if possible. Especially after finding out what each on has done. Also I feel like there may be someone who is curious who Shirou didn't kill among the ancestors. So I'll list the ones he either couldn't kill or didn't want to kill: (1,2,3,4,5,9,14,18,20,21) And the ones he couldn't find: (19,22,23,27) Everyone else you can assume to be dead or sealed, but it the long run it won't affect the story.**

 **Any feedback you can give me is appreciated; there are still a few minor things story wise I'm not sure how to represent. Stuff like how Sans and Papyrus should speak in a story (with sans in all lower case and PAPYRUS IN ALL UPPERCASE) because I don't think Fanfiction lets you use different fonts, and their current formats might be annoying in story form. And stuff like how battles should be portrayed. I have some ideas for both problems, but they are still a work in progress. I'm also toying with the idea that the seal turns whoever enters it into a child to help protect monsters. Some of the things that are brought by the children into the underworld make no sense for a child to have. I could make cases for both sides that I like, but basically it boils down to Shirou becoming a child again would be funny and open the way for a lot of jokes, but could feel contrived if I failed to pull it off right. Let me know what you think!**

 **I'd like to thank you again for reading this first chapter. Have a good day, and stay determined!**


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